1. Field of the Invention
This invention relates to an image processing apparatus appropriate for use in an image processing system which integrates such components as image input units and image output units.
2. Description of the Related Art
There are conceivable various forms of image processing systems comprising image input units, an image processing apparatus, and image output units. A general digital copier is considered the simplest form of image processing system having one unit for each category. By the way, image input and output units has a spatial frequency characteristic; if this spatial frequency characteristic is ignored, it is difficult to provide a high-quality output image.
It is not necessarily proper to flatten the spatial frequency characteristic of the entire digital copier. For example, to output characters, line drawings, etc., it is preferable that edge enhancement be effected. Therefore the gain needs to be raised in a high spatial frequency range. On the other hand, for a halftone dot image like a print original, the gain needs to be lowered to prevent moire in a high spatial frequency range.
Such a gain adjustment is made by the image processing apparatus in the digital copier to provide a desirable spatial frequency characteristic as the whole copier. The desirable spatial frequency characteristic varies depending on the type of input image. For example, an image processing apparatus is also known which assumes the types of input images to be characters, photographs, characters plus photographs, and maps and changes a correction characteristic in response to the detected (or user-specified) image type.
A general image processing system is provided with a plurality of image input units and image output units, one of which is selected as required. In such a case, the spatial frequency characteristic also changes with the selected unit. Thus, an image processing apparatus which selects a correction characteristic responsive to the selected input/output channel is also proposed in Japanese Unexamined Patent Publication No. Hei. 3-88571.
By the way, in the above-mentioned configurations, the person who determines the correction characteristic of an image processing apparatus previously knows the spatial frequency characteristics of image input and output units and sets the optimum correction characteristic for the image processing apparatus in response to the selected image input and units and the input image type. Since it is intricate for the general user to perform such work, generally the engineers of the manufacturer set the correction characteristics.
However, in recent years, networking of image processing machines has been increasing and it has become difficult for the manufacturer to understand what image input and units the user connects to a network. Further, as image input and output units increase, the number of necessary correction characteristic items becomes enormous. For example, assuming that ten models of image input units and ten models of image output units are provided and that the number of image types is four, the number of necessary correction characteristic items becomes 400.
In fact, more correction characteristic items become necessary. For example, most scanners often used as image input units have a plurality of operation modes of "high image quality mode," "high speed mode," etc., and the spatial frequency characteristic also varies depending on the operation mode. With CD-ROM drives, etc., the spatial frequency characteristics of image data stored on CDs, etc., vary although the CD-ROM drive, etc., contains only one operation mode.
That is, the spatial frequency characteristics of image data vary from image data to image data according to the scanners used in the producers of the image data and the production process. In view of the realities, determination of the correction characteristic in response to each input/output channel is technically possible, but is poor in realizability. After all, in network systems, a sufficient correction characteristic adjustment cannot be made and it is difficult to make the most of performance of image input and output units.